1. Technical Field
The present invention relates to a projector which includes a discharge light emission type light source having a pair of electrodes and a driving method of a light source for a projector.
2. Related Art
According to a discharge lamp lighting device for a projector which uses a high pressure discharge lamp, it is known that a projection is formed on the tip surface of each electrode of the lighting device during light emission. However, in such a condition where the lighting device continuously emits light for a long period, a plurality of such projections may be formed or the tip surface of the electrode may be even concaved or convexed. These phenomena lead to instability of the discharge position, causing decrease in illuminance or flickering due to arc shift. For overcoming these drawbacks, a technology currently proposed melts the electrode surface to smooth the tip surface of the electrode (see JP-A-2002-175890). Another related-art technology melts unnecessary projections other than an essential projection as a starting point of discharge to remove the projections (see JP-A-2006-332015 and JP-A-2006-59790).
According to the technology disclosed in JP-A-2002-175890, however, the projections as the starting points of discharge disappear on both sides of the electrodes at the same time. Thus, the distance between the tips of the electrodes increases. In this case, the arc length considerably increases, and light utilization efficiency lowers in optical systems disposed downstream from the electrodes. Moreover, because the starting point of discharge is not determined, flicker and arc shift are easily caused. These conditions lead to flickering—of a projection image or lowering of light utilization efficiency in the optical systems disposed downstream.
The technologies shown in JP-A-2006-332015 and JP-A-2006-59790 do not prevent deformation and shift of the projection which is essential as the starting point of discharge, and thus cannot improve flickering of a projection image and lowering of light utilization efficiency caused by variations in the arc length and arc position resulting from the deformation and shift of the projection.